Nowadays, in order to improve and optimize techniques of neuromotor rehabilitation of limbs of the human body, it is known art to avail of motorized systems able of assisting the patient in the different movements necessary to recover the limb to be rehabilitated.
More precisely, biomedical devices of the robotized type are known which are able of interacting with the patient thus ensuring that the movement of the musculoskeletal apparatus follows the physiological movement of the treated limb and of the joints involved in the movement, while at the same time providing a breadth of movement that is as extensive as possible, within the limits of the actual movements performed by the limb affected by rehabilitation.
In particular, for the upper limbs of the human body, biomedical devices of the motorized type for neuromotor rehabilitation are known which substantially comprise an exoskeleton that can be fitted over the patient's upper limb to be rehabilitated, and are composed of two or more rigid rods which are articulated to each other with a plurality of degrees of freedom and are provided with a plurality of electric motors which are adapted to help the patient to perform the movements necessary for rehabilitation.
In more detail, conventional robotized biomedical devices for neuromotor rehabilitation of the upper limb are provided with a first rigid rod, to which the arm of the patient is attached, and which is articulated to the supporting structure by way of a first mechanical joint that is able of replicating, as far as is possible, the physiological movements of the shoulder, and a second rigid rod, to which the forearm of the patient is attached and which is articulated to the first rigid rod by way of a second mechanical joint for replicating the movements of the elbow joint.
In some cases, the second rigid rod is serially coupled to a mechanical joint, that can be gripped by the patient, in order to enable the rehabilitation of the physiological movements of the wrist.
The robotized biomedical devices of the known type suffer two critical aspects. The first consists in the intrinsic singularity of the exoskeletal structure in the event of complete extension of the forearm (alignment of the arm-forearm axis) and the second consists in the approximation of the movement of the shoulder girdle and thus of the real center of instantaneous rotation of the arm (movement of the head of the humerus with respect to a fixed outer system of reference).
As can be seen in several devices, the kinematic singularity that can arise if arm and forearm are aligned does not allow the patient, in certain defined rehabilitation sessions, to modify the rotation axis of the elbow (and thus to perform movements of inner/outer rotation of the shoulder about the axis of the arm) with the forearm extended, since the kinematic singularity of the exoskeleton would not allow the exoskeleton to modify the configuration of its joints consistently and to keep the axis of the exoskeleton corresponding to the flexion/extension of the elbow aligned with the actual rotation axis of the elbow joint. A loss of mutual parallelism of these axes owing to a corresponding rotation about the axis of the arm would have an impact on the effective reversibility of the exoskeleton at the elbow.
Moreover, the head of the humerus, which can be identified as the center of instantaneous rotation of the shoulder, in general physiologically performs a combined movement of rotary and translational motion owing to the movement of the shoulder girdle in the three Cartesian dimensions and simplifying it with compound movements characterized by one or two degrees of freedom is an approximation.
Nevertheless, the articulation of the shoulder is viewed, in some relatively simple conventional devices, as a merely spherical joint without taking account of the actual kinematic movement of the shoulder girdle. In fact in the exoskeleton, i.e. in the kinematic structure that can be applied to the patient, rotations about three concurrent axes are possible, but translational motions of the center of instantaneous rotation are not possible.
Some more advanced robotized biomedical devices comprise means designed to shift the center of instantaneous rotation of the exoskeleton, in order to allow the combined rotary and translational motion of the actual center of instantaneous rotation of the shoulder.
For example, robotized biomedical devices are known in which the center of instantaneous rotation can rotate about an axis, thus approximating the trajectory described by the actual center of instantaneous rotation with an arc of circumference. In this type of biomedical device, despite the rotation made possible in the center of instantaneous rotation, there are still limits on the possible movements of the shoulder girdle.
A development of the robotized biomedical device just described makes it possible to perform two distinct rotations about two axes that are perpendicular to each other in the center of instantaneous rotation. In this way, the shoulder enjoys five degrees of freedom, thus achieving a good solution in kinematic terms.
In another example of robotized biomedical devices of the known type, the center of instantaneous rotation can perform vertical translational movements in following the variations of the actual center of instantaneous rotation of the shoulder.
Thanks to the construction of these devices, this compensation is along the vertical direction only, i.e. in the direction that is still the most appreciable for the problem under discussion.